by
George Frederick Linde
Thesis presented in partial fulfilment of the requirements for the degree of Master of Engineering in the Faculty Engineering at
Stellenbosch University
Supervisor: Dr GA Oosthuizen Faculty of Engineering
i
Declaration
By submitting this thesis, I, the undersigned, hereby declare that the work contained in this thesis is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification.
___________________________ _________________________
G F Linde Date
Copyright © 2016 Stellenbosch University All rights reserved
ii Abstract
In the agricultural industry there are different wear problems that need to be managed in order to extend the operating life of equipment. The agricultural industry is a great asset to all South Africans in terms of food production and employment. Purchasing and maintaining agricultural machines and equipment are major cost items for agri businesses. There are many problem areas in this industry and the people carrying the consequences include farm equipment manufacturers, farm contractors, farmers and organisations that process the harvested crops in agro-processing. Equipment used in various applications is subject to different kinds of wear caused by different materials in different operating conditions.
The focus of this research is limiting wear, mainly caused by grain (maize and wheat), during agro-processing and transformation in storages, such as silos. Wear problems occur in mills and silos where grain is stored in large quantities and moved through the process of agro- processing. There are different ways and methods of limiting wear and increasing the performance of the equipment used in the agricultural industry.
Different thermal spray coatings were tested to evaluate their ability to limit the wear that may causes a decrease in the performance of the equipment in agro-processing. Different coatings of tungsten carbides and chrome oxides and carbides were sprayed onto five specimens using different thermal coating processes. The behaviour of these different coatings was tested by objecting them to constant wear. The constant wear was applied using silicon carbide grinding stone that was mounted to a Dremel tool. The Dremel tool was mounted to a CNC machine to control the grinding parameters. The experiment tested the coatings under constant conditions before they were installed into a silo, to test the coatings in a real world application. The objective of the research was to find the balance between the cost and performance of the different coatings.
iii Opsomming
In die lanboubedryf is daar ‘n groot behoefte om wrywingsprobleme te beperk en sodoende die lewensduur van die toerusting te verleng. Die landboubedryf is ‘n groot aanwins vir Suid-Afrika in term van voedsel produksie werkskepping wat van die mees algemene probleme in die land is. Aankoop en onderhoudskostes van masjiene en toerusting wat gebruik word is van die duurste kostes in die lanboubedryf. Daar is verskeie probleem areas in die bedryf en sluit die vervaardigers van lanndbou toerusting, plaas kontrakteurs, boere en organisasies wat graan verwerk na dit geoes word in. Toerusting wat gebruik word in verskillende toepassings, ervaar verskillende tipes wrywing wat veroorsaak word deur verskillende faktore in verskillende werksomstandighede.
Die studie het hoofsaaklik gefokus om die problem, wat ondervind word by graansilo’s en meulens waar graan in groothoeveelhede gestoor en vervoer word, te beperk. Daar is menigte plekke, soos die graan vanaf die aflaai punt tot binnekant die silo beweeg, waar wrywing voorkom tussen metaal en die bewegende graan. Daar is veskillende maniere en metodes om wrywing te beperk en die werksverrigting, van die toerusting gebruik in die landboubedryf, te optimiseer.
Verskillende termiese sproei bedekkings is getoets om die wrywing, wat die werksverrigting van die toerusting verminder en verkort tydens die verwerking van graan, te beperk. Verskillende bedekkings van wolfram- en chroom oksied en karbiedes is deur termiese sproei prosesse toegepas om vyf toetsplate. Die gedrag van die bedekkings is geoets teen konstante weerstand. ‘n Silikon karbied slypsteun was monteer aan die onderkant van ‘n Dremel gereedskap om wrywing toe te pas op die bedekkings. Die Dremel gereedskap met die slypsteun gemonteer was installeer op ‘n CNC masjien om die wrywingsproses toegas deur die slypsteun te beheer. Die eksperiment was gebruik om die bedekkings te toets in konstante toestande voordat dit installeer was by ‘n silo waar wrywing en onderhoudskostes ‘n groot probleem is, om die bedekkings te toets in ‘n regte-wereld toepassing. Die doelstelling van die studie was om die middelpunt te kry tussen die koste en weerstand teen wrywing van die verskillende bedekkings.
iv Acknowledgements
I would like to thank Dr GA Oosthuizen for the guidance he has given me throughout this project.
A special thank you to Mr Jacques Willmot, operational manager at Nova Foods in Malmesbury for the opportunity to run this project at Nova Foods and for the supply of the equipment.
This study would not have been possible without the work done by Dr Jan Lourens, managing director and Paul Young, production manager of the spray workshop at Thermaspray in Johannesburg, for the supply of the coatings during this project.
Finally, I would like to thank my family, especially my parents, for all the support, love and guidance through the past few years. If it was not for your belief in me I would not be where I am today.
v Table of Contents Declaration ... i Abstract ... ii Opsomming ... iii Acknowledgements ... iv Table of Contents ... v
List of Figures ...vii
List of Tables ...ix
Nomenclature ... x
Chapter 1 Introduction... 1
1.1 Background ... 1
1.2 Problem statement ... 1
1.3 Research objectives ... 2
1.4 Limitations and assumptions ... 2
1.5 Research approach ... 2
1.6 Reading this document ... 3
Chapter 2 Problem Areas of Wear Corrosion in the Agriculture Industry ... 4
2.1 Introduction ... 4 2.2 Soil cultivation ... 4 2.3 Roller bearings ... 6 2.3.1 Tractors ... 6 2.3.2 Balers ... 7 2.3.3 Combines/Harvesters ... 7
2.4 Tribology in bulk solids handling... 8
2.4.1 Transportation pipes at storage centres ... 8
2.4.2 Transportation system at production centres ... 9
2.5 Corrosion caused by agricultural chemicals... 11
2.5.1 Fertilisers ... 11 2.5.2 Silage ... 12 Chapter 3 Wear ... 15 3.1 Background ... 15 3.2 Abrasive wear... 16 3.3 Adhesive wear ... 17 3.4 Erosive wear ... 18
Chapter 4 Methods of Wear Testing ... 20
4.1 Traditional methods ... 20
4.2 Wear of engineering material ... 20
4.3 Wear test methods ... 21
4.3.1 Abrasive and adhesive test equipment ... 21
4.3.2 Pin-on-disc ... 22
4.3.3 Rubbing tests ... 22
vi
4.4 Experiment theory ... 23
Chapter 5 Performance Enhancement Strategies ... 24
5.1 Opportunities in plastic ... 24
5.1.1 Stanyl wear and friction applications... 24
5.2 Rubber and urethane ... 25
5.2.1 Tuff-Tube spout lining ... 25
5.2.2 Spray urethane ... 26
5.3 Rubber sheets ... 27
5.4 Thermal spray coating technology ... 28
5.4.1 Coating processes ... 28
5.4.2 Coating selections on different types of wear ... 30
Chapter 6 Research Problem Statement and Research Objectives ... 31
6.1 Problem statement ... 31
6.2 Research objective ... 32
6.3 Importance of the research study ... 33
6.4 Limitations and assumptions of the study ... 33
Chapter 7 Research Methodology ... 34
7.1 Background ... 34
7.2 Applying thermal spray coating technology ... 34
7.2.1 Tungsten Carbide, Cobalt Chrome and fine carbides ... 34
7.2.1.1 1350VM (WC-Co-Cr) Tungsten Carbide Cobalt Chrome... 35
7.2.1.2 3652FC (WC-Co-Cr) Tungsten carbide cobalt chrome with fine carbide distribution ... 36
7.2.2 Chromium oxide ... 36
7.2.2.1 6156 (Cr2O3) Chrome oxide powder ... 37
7.2.3 Chromium carbide ... 37
7.2.3.1 5241 (CrC) Chrome carbide – Nickel Chrome powder ... 38
7.2.4 140MXC Nano composite wire sprayed with the arc spray system and polished to remove high spots, the wire contains iron, chrome, molybdenum, tungsten and other trace elements ... 39
Chapter 8 Experimental Setup and Design ... 41
8.1 Experiment setup ... 41
8.2 Grinding setup ... 41
8.3 Measurement of wear ... 45
Chapter 9 Results and Discussion ... 50
9.1 Wear performance in the form of volume loss ... 50
9.2 Wear performance versus costs ... 52
9.3 Discussion ... 53
Chapter 10 Industrial Application ... 55
10.1 Installation... 55
10.2 Results ... 56
Chapter 11 Conclusion ... 57
Appendix A G-code Use in CNC Machining with Dremel Tool ... 60
Appendix B Dremel 4000 Rotary Tool Overview ... 61
vii List of Figures
Figure 2.1 Typical wear in soil cultivation. a) Ripper to break hard soil. b) Plough used to prepare a
decent seeding bed (Soil Cultivation-Ploughing) ... 4
Figure 2.2 Roller bearings on tracks that are used in place of tyres on tractors with high horsepower (Tracklayers ... 6
Figure 2.3: a) Cutting drum with counter blade and b) a round baler ... 7
Figure 2.4: a) Wearing parts in the crop flow area and b) a self-propelled harvester... 8
Figure 2.5: Curve-sectioned chute of rectangular cross... 9
Figure 2.6: Result of the transport of bulk materials in a coal fired power station ... 9
Figure 2.7: Typical bins on bulk production and storage plants ... 10
Figure 3.1: Two and three-body modes of abrasive wear ... 16
Figure 3.2: Schematic illustration of adhesive wear ... 18
Figure 3.3: Illustration of the different types of erosive wear ... 19
Figure 4.1: Schematic diagram of the Taber abrasion apparatus ... 23
Figure 5.1: Applications of Tuff-Tube Spout Lining (Urethane Spout Liner to Protect Equipment from Extreme Spouting Wear) ... 26
Figure 5.2: a) 40 ton dump truck with urethane for increased load release b) Lined steel hopper (Urethane Spout Liner to Protect Equipment from Extreme Spouting Wear, n.d) ... 27
Figure 5.3: Assorted rubber plates (Rubber & Urethane Products Extend the Life of Equipment in the Agricultural Industry) ... 27
Figure 6.1: Diagram of processes at a silo for grain storage: 1 Checking; 2 Hopper; 3 Vertical handling; 4 Cleaning; 5 Weighing; 6 Insecticide treatment; 7 Horizontal handling; 8 Temperature control ... 32
Figure 7.1: Flowchart of the research methodology ... 34
Figure 8.1: Five different research coatings on the testing specimens ... 41
Figure 8.2: Dremel mounted to CNC machine ... 42
Figure 8.3: a) Aluminium oxide and silicon carbide cylindrical stone b) Schematic drawing of the grinding stone with dimensions ... 44
Figure 8.4: a) The grinding process on the coatings b) Schematic drawing of the grinding process . 45 Figure 8.5: The three surface roughness components that exist simultaneously (Tool Design) ... 46
Figure 8.6: The Mitutoyo Surftest: 211 surface roughness tester... 47
Figure 8.7: Schematic presentation of the coated specimen with ground grove ... 47
Figure 8.8: Schematic presentation of where the surface roughness test was done ... 48
viii Figure 9.1: Graph of performance vs cost ... 53 Figure 10.1: The eroded metal guide relaced at Nova Foods with different coatings ... 55 Figure 10.2: Five different coatings on the different platesmounted to the grain guide ready for
installation ... 56 Figure 10.3: The eroded plates after 4 000 tons of grain was guided through them ... 56
ix List of Tables
Table 7.1: Different researched coatings used ... 40
Table 8.1: Grinding parameters ... 43
Table 9.1: The Rt surface roughness values of the research coatings [µm] ... 50
Table 9.2: Volume loss calculated per pass for the different coatings [mm3] ... 51
Table 9.3: The percentage volume loss per pass of the total coating on the ground area... 51
x Nomenclature
Acronyms
APS Atmospheric plasma spraying GDP Gross Domestic Product
Ha Hectares
HVOF High Velocity Oxy-Fuel Spray
RH Relative Humidity
PPA Polyphthalamide
PA6T Polyamide 6T
PA9T Polyamide 9T
PPS Polyphenylene sulphide LCP Liquid Crystal Polymer
FAOSTAT The Food and Agriculture Organization Corporate Statistical Database ASAE/ASABE American Society of Agricultural and Biological Engineers
VPS Vacuum plasma spraying
SPE Solid particle erosion
Terminology
Agro-processing The process grain is going through from when it is harvested to be processed
Glossary
Spindle speed, RPM [ Revolutions per minute] Cutting speed, Vc [mm / min]
Temperature, ˚C [Degrees Celsius]
1 Chapter 1 Introduction
1.1 Background
Agriculture contributes around 10 percent of South Africa’s formal employment; it provides work for casual labourers and contributes around 2.6 percent of gross domestic product (GDP) for the nation. According to the Food and Agriculture Organization Corporate Statistical Database (FAOSTAT), South Africa is the world's fourth highest producer of chicory roots and grapefruit; the fifth highest producer of cereals; the seventh highest producer of green maize and maize; the ninth highest producer of castor oil seed and pears; and the world’s tenth highest producer of sisal and fibre crops. The South African dairy industry has about 4 300 milk producers providing employment for 60 000 farm workers and contributing to the livelihoods of around 40 000 others. (AgriSeta, 2010)
Grains and cereals are South Africa's most important crops and in the 1990s already occupied more than 60 percent of hectares under cultivation. Maize is the country's most important crop and approximately eight million tons of maize grain is produced in South Africa annually on almost 3.1 million ha of land. Half of the production consists of white maize, for human food consumption. It is a dietary staple, a source of livestock feed and an export crop. Generous financial and extension services from government programmes are crucial to the country's self-sufficiency in this enterprise. Maize is grown commercially on big farms, and on more than 12 000 small farms, primarily in the North West Province, Mpumalanga, the Free State and KwaZulu-Natal. Maize production generates at least 150 000 jobs in years with good rainfall and uses almost one-half of the inputs of the modern agricultural sector (Plessis, 2003).
1.2 Problem statement
Machinery, equipment and the maintenance of machinery and equipment are major cost items in the agricultural industry. Purchasing and maintaining agricultural machines are two of the most substantial costs in the agricultural industry, which includes farm equipment manufacturers, farm contractors, farmers and organisations who handle the harvested crops through agro-processing. An important consideration in farm management is the optimal production time lost during equipment replacement. (Aldo Calcante, 2013)
2 The problem this research focuses on is mainly wear caused by grain (maize and wheat) during agro-processing and transformation in storages like silos. Wear problems occur in mills and silos where grain is stored and moved in large quantities through the process of agro- processing.
1.3 Research objectives
The main objective of the project was to identify a coating which will increase the operating life and decrease the maintenance cost of equipment in the agricultural industry. Different thermal spray coatings were tested to limit the wear that mainly causes a decrease in performance of equipment in agro-processing. Different coatings of tungsten carbides and chrome oxides and carbides were sprayed onto five specimens by different thermal coating processes. The behaviour of these different coatings were tested against constant wear. The different coatings were compared mainly on wear resistance against cost.
1.4 Limitations and assumptions
As stated in the research objective, five different coatings were tested. These coatings were applied by a service provider that has all the necessary equipment, tools, machines and coating materials. The coatings, experiment and application used to test the performance of the coatings in the research study, and the results obtained, should be applicable to other applications in the industry. It would be too expensive to test each application separately and draw conclusions from each individual application. The chosen application had to be one that could be relevant to other equipment and other sections of the agricultural industry.
1.5 Research approach
In order to complete the research objective, a specified approach was followed during this study. This approach needs a comprehensive literature review concerning all the aspects that need to be considered for the testing and evaluation of different coatings to resist wear in the agricultural industry. The problem areas in the industry must be thoroughly investigated. The type of wear that occurs in each problem area must be identified to select the suitable coating for the right application. The coatings have different mechanical properties and respond differently to different types of wear. The working conditions in which the coating should operate must also be investigated and they will have an effect on choosing the right coating for the application.
3 To pilot a real world application in an experiment, all the factors in the real world application, must correspond to the factors in the experiment. The best coating according to the objective must be installed where the most extreme conditions will occur.
1.6 Reading this document
Chapter 2 discusses the literature dealing with problem areas of wear and the type of wear that occurs. In chapter 3, the different types of wear occurring in the agriculture industry are described in more detail in order to understand the type of wear that occurs in specific problem areas in the industry. Different methods of testing wear are investigated in chapter 4. Chapter 5 describes the different enhancement strategies that can be applied to limit wear in equipment, and extend the operating life of the equipment. The problem statement and research objective are explained in more detail in chapter 6. Chapter 7 describes the research plan and methodology that were used in this study. The experimental design and setup are described in detail with the help of some figures to explain the experiment in Chapter 8. The results, as well as the discussion and interpretation of the results, can be seen in chapter 9. Chapter 10 provides a short description of an industrial installation and the actual results obtained during the real world industrial testing. Chapter 11 sums up the research and presents the main conclusions from the experiment and results.
4 Chapter 2 Problem Areas of Wear Corrosion in the Agriculture Industry
2.1 Introduction
In this chapter different wear and corrosion related problem areas in the agricultural industry are investigated through research and review of previous studies. Agricultural machinery and tools must endure stressful working conditions of continuous wear and tear, with field work exposing equipment to severe abrasion. In agriculture the two main reasons for replacing machinery or equipment are upgrading old equipment and replacing equipment due to wear and corrosion. Corrosion is the deterioration of material by chemical interaction with its environment. Failures of various kinds and the need for expensive replacements may occur even though the amount of metal destroyed due to corrosion is quite small.
2.2 Soil cultivation
Agricultural machinery and equipment used in soil cultivation is exposed to continuous wear and stress. During tough and challenging field work, the machinery is susceptible to abrasion. Larger implements and more powerful tractors operating at higher ground speeds, creates an increased demand for wear resistance on the structural components. Agriculture equipment requires tough and hard, but also flexible, steels to increase the operating life of the equipment and decrease the frequency and cost of replacement (production cost) of worn parts. A major portion of the energy and wear losses in agricultural machinery can be attributed to the movement of tools in soil. The quantity of soil moved each year by these tools is enormous. Although the depth seldom exceeds 100mm, the areas involved are extensive.
Figure 2.1: Typical wear in soil cultivation. a) Ripper to break hard soil. b) Plough used to prepare a decent seeding bed (Soil Cultivation-Ploughing, n.d.)
5 During ploughing, farm implements are worn down by the abrasive action of sand and stone particles present in the soil. This is the most common cause of damage of agricultural machinery. Dry lands cause the wear and tear to be more severe than in irrigated land. (Kumar & Gupta, 1995)
The wear of agricultural tools in the majority of the publications reviewed, was defined simply as a process of abrasion. No additional factors, other than mechanical ones, were taken into account. Only a few researchers have taken the acidity of soil into account. The considerable content of salt, acids, and hydrocarbons at a significant degree in moist soil, accelerates the processes of the wear and corrosion on tools working in moist soil.
During contact with soil agricultural tools such as shares, mouldboards or the teeth of harrows, undergo abrasion, mainly by friction. Soil is a mixture of mineral particles as well as organic and inorganic compounds of hydrogen with very varied composition and tribological proprieties. With regard to variable composition, the moisture and temperature of soil, the investigation of wear processes is difficult. The process of wear, which is a mechanical abrasion intensified by the chemical influence of the environment, can be treated. The intensity of mechanical abrasion of the tool by sharp grains of sand depends on their geometry and the difference of hardness between the abrasive medium and the material of the tool (Stabryla, 2007).
Metal wear in agriculture tools is an old, but ongoing problem. Wear is the main element which determines the lifespan of a soil engaging tool. The efficiency of the tool and its work capacity are also determined by the soil’s response to the tool. The research on wear has mainly been concentrated on industrial materials related to large industries. In the agriculture sector, however, the soil engaging tools have received little attention (Kushwaha & Shi, 1989).
Farmers and equipment operators often complain about the high wear rate of ground engaging tools in some dry land agricultural areas. Farmers face problems with recurring labour, downtime and the replacement costs of exchanging the worn down ground engaging components like ploughshares. Worn out tools results in poor tillage and seeding efficiency and higher fuel costs. Carbon or low alloy steels are generally preferred to make tillage tools that are under low stress abrasive wear. Tillage having composites with alumina ceramics and
6 boron, medium and high carbon heat treated steels, offers great potential for the severity of abrasive wear in soil-engaging components. The hardness of the tillage tool, grain structure and its chemical composition are also influential factors in determination of the wear rate. Wear due to highly abrasive soils has surface damage characterised by scoring, cutting, deep grooving and gauging, and micro machining caused by soil constituents moving on a metal surface (Parvinkal & Navjeet, 2015).
2.3 Roller bearings 2.3.1 Tractors
There is an increased reliability and more horsepower to the ground in tractors with the new track treads used as tyres on tractors with high horsepower. Roller bearings used in critical areas such as driveline positions, gear cases, and wheel shafts are required to have greater power densities, and an ability to operate longer at higher loads. Roller friction and shock loads transmitted from the track chain create heat in the interior of rollers and on the roller surface and this can cause wear. Track treads will show increased wear rates, compared to machines running on tyres, when operated on hard surface roads. Tracks, however, show much reduced wear rates when operating in the field (Hill, 2008).
Most tractors do not work on level ground at all times and the wear rate for the inner and outer track roller flanges is often different. This can be the result even if all the undercarriage components are in alignment and the wear of the track roller flanges is within the correct limits. Worn mounting bearings and bent diagonal brace or roller frames cause the variable wear between inside and outside roller flanges and idler flanges and rail sides. Figure 2.2 shows two photos where typical wear problems occur in tractors with track treads (Hill, 2008).
Figure 2.2: Roller bearings on tracks that are used in place of tyres on tractors with high horsepower (Tracklayers, n.d.)
7 2.3.2 Balers
Hay and forage machines are subjected to wear primarily at points which get into intensive contact with the crop, which includes all types of blade, but also sheet metal channels through which the crop is past at high speed. See figure 2.3(a). A baler is a piece of farm machinery used to compress a cut and raked crop into compact bales that are easy to handle, transport, and store. Balers operate in a constant swirl of dust shown in figure 2.3(b). Roller bearings that support pulleys, drive systems, and augers inside balers are often damaged by debris that finds its way inside the bearing. Hay baling is a very dusty operation. Dust and plant material collect in all nooks and crannies of the machine. This material then collects moisture, which over time causes rust and corrodes the surfaces of the machine (Martensen).
Figure 2.3: a) Cutting drum with counter blade and b) a round baler (Martensen)
2.3.3 Combines/Harvesters
Combines are idle for much of the year. They are operated at full capacity for short periods of time only. Roller bearings in combines need to be dependable with the ability to operate in dusty, dirty, and harsh conditions. There are especially hard conditions for forage harvesters, in which a lot of sand and dust are taken in along with the maize. Further downstream, the maize then passes the so-called corn cracker, which consists of two fast rotating toothed rollers, which are located at a very close distance to each other. When passing through this gap, the maize corns are squeezed for better digestibility. These rollers are also subjected to a high degree of wear (Doll & Eckels).
8 The cam follower rollers of the tine arms run in this cam track, which takes place under high surface pressure and very dusty conditions. In the forage harvester, the maize is cut between the moving blades of the cutting drum and the stationary counterblade (A in Fig. 2.4 a). On account of the high throughput capacities of these machines, wear occurs after a relatively short period of time. The forage passes through a feed channel chamber (B in Fig. 2.4 a) behind the cutting drum, which is normally made of a very hard material on the lower side to ensure protection against wear (Martensen).
Figure 2.4: a) Wearing parts in the crop flow area and b) a self-propelled harvester (Martensen).
2.4 Tribology in bulk solids handling
2.4.1 Transportation pipes at storage centres
Wear in bulk materials handling plants may result from impact or abrasion or, as is often the case, a combination of the two. Wear is caused by grain in operations where bulk grain (large quantities) is handled. Normally at a silo where grain is stored, wear occurs throughout the process from the hopper where the trucks dump it, all the way to the particular silo it has to be moved to on conveyers. This process is also called agro-processing.
Erosive wear due to impact occurs when streams of bulk solid particles impinge, usually at medium to high velocity, on inclined surfaces. Typical examples include the intake end of chutes, and bin and hopper walls subject to impact loading during filling. In the case of pneumatic conveyor systems, erosive bend wear can be quite substantial due to the high velocity of particles in the air stream (Johanson, 1995).
9 Abrasive or rubbing wear occurs when the bulk solid flows along the walls of bins and chutes. Wear in this case is a combination of pressure and rubbing velocity. Abrasive wear assumes that the wear results from a direct relation between the normal pressure, the friction coefficient and the rubbing velocity (Roberts & Oomsm, 1985).
Figure 2.5: Curve-sectioned chute of rectangular cross (Ghadban, 2010)
2.4.2 Transportation system at production centres
Throughout the world bulk materials handling operations perform a key function in a great number and variety of industries. While the nature of the handling tasks and scale of operation vary from one industry to another and, on the international scene from one country to another, according to the industrial and economic base, the relative costs of storing, handling and transporting bulk materials are, in the majority of cases, very significant. It is important, therefore, that handling systems be designed and operated with a view to achieving maximum efficiency and reliability (Roberts, 1990).
Figure 2.6: Result of the transport of bulk materials in a coal fired power station (Bulk Terminals and Ports, n.d.)
10 Over the past three decades much progress has been made in the theory and practice of bulk solids handling. Reliable test procedures for determining the strength and flow properties of bulk solids have been developed and analytical methods have been established to aid the design of bulk solids storage and discharge equipment. There has been wide acceptance by industry of these tests and design procedures and, as a result, there are numerous examples throughout Australia of modern industrial bulk solids handling installations which reflect the technological developments that have taken place (Roberts, 1990).
Notwithstanding the current situation, the level of sophistication required by industry demands, in many cases, a better understanding of the behaviour of bulk solids and the associated performance criteria for handling plant design. In particular, reliability and equipment life are important considerations and, in this respect, the study of tribology as it relates to handling plant design and performance is of great significance. In view of the importance of friction, adhesion and wear in the flow of bulk materials in bins, feeders and chutes there is a need for greater attention to be focused on this area of tribology (Roberts, 1990).
The efficient operation of bulk solids handling plant depends, to a significant extent, on the smooth flow and handling of the bulk solids without blockages occurring in bins and chutes. See figure 2.6 for a typical example of the effect of wear on a section of equipment used in bulk solids handling. It is important, therefore, that handling plants are designed taking into account the relevant flow properties of the bulk solids being handled. In this respect it is important that the significant influence of wall friction, cohesion and adhesion be understood and taken into account when designing bins and chutes (Roberts, 1990).
11 Procedures for determining these parameters are well established and documented in several articles. The selection of appropriate lining materials for bins and chutes, in addition to the need for favourable frictional properties, should also provide long wear life. The role of accelerated wear tests to evaluate lining materials as an adjunct to the established procedures for flow property determination is an important one (Roberts, 1990).
2.5 Corrosion caused by agricultural chemicals
Corrosion is the deterioration of materials by chemical interaction with their environment. The consequences of corrosion are many and varied. The effects of these on the safe, reliable and efficient operation of equipment or structures are often more serious than the simple loss of a mass of metal. The two main reasons for replacing machinery or equipment include upgrading old equipment and replacing it because of wear and corrosion (Oki & Anawe, 2015).
Furthermore, there are many commercial chemicals used on farmlands. These include: grain and silage preservatives; pest and weed control; and proprietary acid solutions for cleaning dairy equipment. In addition to these, farm wastes and slurries contain many chemicals which can also be particularly corrosive. The aim of this discussion is to proffer suitable solutions to corrosion occurring due to the actions of these agricultural chemicals (Oki & Anawe, 2015).
Agricultural buildings and facilities largely differ from the common ones in the enormously aggressive environment (animal production facilities) or in the fact that they are used to store aggressive chemicals (stores of chemical fertilizers) and satisfactory results cannot be achieved even by preventing the access of outer atmosphere. Here it is worth pointing out that hardly any agricultural enterprise is concerned with the protection of their machines and equipments against corrosion and it is therefore adviced to consider whether their untimely damage or devaluation cannot be prevented by proper storage and conservation. The costs of preserving agents are negligible as compared with the costly machines and considerable savings can be made on repairs. (M. AUGUSTIN, 2003)
2.5.1 Fertilisers
Fertilisers are chemicals given to plants in order to promote growth. They are usually applied either via the soil or by foliar spraying. Fertilisers typically provide, in varying proportions, the three major plant nutrients (nitrogen, phosphorus and potassium) and secondary plant
12 nutrients such as calcium, sulphur, magnesium and iron. Some fertilisers are more corrosive than others, especially if they decompose or react to produce aggressive substances such as ammonia or hydrogen sulfide; if chloride ions are present (including potassium or ammonium chloride), or if acidic conditions prevail. For example, dihydrogen ammonium phosphate or ammonium nitrate can lead to increased corrosion via hydrolysis to acids (Corrosion control of Agricultural Equipment and Buildings, 2010).
The relative ratios of the essential plant nutrients can influence the corrosiveness of compound liquid fertilisers, there being some evidence that the greatest effects occur with fertiliser solutions containing about 15% nitrogen, especially when half the free nitrogen is derived from urea and half from ammonium nitrate. If fertilisers are kept dry, then no corrosion occurs, but being hygroscopic they can pick up moisture and hence may become corrosive. The hygroscopic point is the relative humidity at and above which moisture is absorbed, and varies from one compound to another, and the lower its value, the more corrosive the fertiliser is likely to be. Ammonium nitrate starts to absorb moisture at 60% RH, while certain phosphates absorb moisture only above 90% RH. Moisture initially causes caking of the fertiliser, which can increase its abrasive properties (Corrosion control of Agricultural Equipment and Buildings, 2010).
2.5.2 Silage
Silage is fermented, high moisture forage that is fed to ruminants, cud-chewing animals like cattle and sheep. It is fermented and stored in a structure called a silo. Silage undergoes anaerobic fermentation, typically beginning about 48 hours after the silo is filled. The fermentation is essentially complete in about two weeks. The fermentation process releases a liquid. The amount of liquid can be excessive if there is too much moisture in the crop when it is ensiled. Silo effluent contains nitric acid (HNO3) making it corrosive. It also can be a contaminant of lakes and streams, because of the high nutrient content, and could lead to algae blooms. Silage effluent is potentially one of the most damaging effluents produced by agriculture. There are specific storage instructions to prevent silage leakage. Silage effluent is also very acidic and therefore the storage structures must be resistant to corrosion and acid attack (B.Eker, 2005).
Modern steel silos, both galvanised and glass-coated, are virtually always designed for silage and grain storage. Their adaptation is primarily one of installing aeration equipment, modifying unloading if necessary, and making provision for aeration air discharge in the top
13 of normally sealed units. Older style steel silos, especially those that show severe corrosion in the lower sections and/or those that have not been used for a number of years, should be viewed with extreme caution as safe grain or silage storages. Corrosion on a very thin metal wall can markedly reduce the metal area remaining to sustain the storage load (B.Eker, 2005).
Furthermore, tower silos are prone to corrosion damage, primarily by the organic acids that are produced during the process of ensilage. The most acidic and corrosive environment is claimed to exist within silos containing whole crop maize silage, which ferments readily and rapidly to produce acids with typical concentrations in solution of 2% lactic acid and 0.5% acetic acid and with the pH as low as 3.6. Lactic acid is regarded as the stronger acid and, if oxygen is present also, then secondary fermentation can occur, giving silage, which is predominantly butyric acid, thus yielding a higher pH value (B.Eker, 2005).
In addition, temperatures inside silos can be as high as 30˚C, so corrosion rates inside tend to be higher than those on the external walls. In practice, the contact time for acids on machinery like augers and balers is low, therefore, corrosion rates are usually less than 1 mm per year (on mild steel) (Corrosion control of Agricultural Equipment and Buildings, 2010).
Materials that have given good service for silos are aluminium (over 10 year’s life), and vitreous enamelled steel, which is particularly easy to clean and maintain. Plastic coatings are liable to surface damage, and crevice corrosion can occur if adhesion is lost. Galvanised steel may deteriorate in contact with silage juices and slurries, but is resistant to silage vapours (Corrosion control of Agricultural Equipment and Buildings, 2010).
The order of preference for metals of construction for storage vessels is: aluminium (best), followed by galvanised steel, and mild steel. The combination of abrasion and acid attack is also especially destructive to concrete because acids react with lime. Covering floors with plastic sheeting, or with an acid resisting coating such as chlorinated rubber or epoxy paint, provides protection (Corrosion control of Agricultural Equipment and Buildings, 2010).
All agriculture equipment requires coating that resists wear and corrosion in their applications. For this reason corrosion must be prevented by adopting some reusable friendly methods. Besides, certain inhibitors can be used for corrosion protection in agricultural applications. Corrosion control and prevention can be accomplished by keeping equipment clean and dry after each use, applying corrosion-resistant materials or materials with a
14 corrosion allowance, applying external coatings (paints) or internal lining systems, or using cathodic protection. Strategies for maintaining and optimising inspection programmes for agriculture equipment with a high corrosion risk need to be developed. Development of new and improved inspection techniques is required to ensure the integrity of agricultural equipment (Eker, 2005).
In practice, the contact time for acids on machinery, augers and balers, is low, so corrosion rates are usually small. During storage, acid-treated grain has little effect, the major precaution needed being to minimise the risk of concentration in local areas such as crevices, or where stagnant pools of liquid can collect. Propionic acid is highly corrosive, but little damage should occur if correct precautions are taken, such as the complete removal of the acid-treated grain from the silo after use, washing with water, and avoidance of contact of treated grain with unprotected machinery. (Corrosion control of Agricultural Equipment and Buildings, 2010)
15 Chapter 3 Wear
3.1 Background
Dorfman and Mitchell define wear, in an article, as “The unwanted removal of material from a surface as a result of mechanical action. Mastering the wear process means controlling a complex set of system and process variables.” This starts with a clear understanding of the component, its material history (grain size, processing, alloy chemistry, surface hardness), the type of wear the component will see, and the type of environment. Each type of wear has a corresponding specific wear mechanism (Dorfman, 2002).
Wear is a determined service condition in many engineering applications with important economic and technical consequences. The effect of abrasion wear is particularly evident in the industrial areas of agriculture, mining, mineral processing, and earth moving. Wear is a critical concern in many types of machine components and is often a major factor in defining or limiting the suitable lifetime of a component.
Wear results from contact between a surface and a body or substance that is moving relative to it. Wear is progressive and increases with usage or increasing amounts of motion. It results in the loss of material from a surface or the transfer of material between surfaces (Bayer, n.d.).
Wear failures occur because of the sensitivity of a material or system to the surface changes caused by wear. It is the geometrical aspects of these changes, such as a dimensional change, a change in shape, or residual thickness of a coating, that cause failure. Changes in appearance and the nature of the wear damage can be causes for failure as well. The same amount or degree of wear may or may not cause a wear failure; it is a function of the application. For example, dimensional changes in the range of several centimetres may not cause wear failure on excavator bucket teeth, but wear of a few micrometres might cause failure in some electromechanical devices. As a consequence of these differences, there is no universal wear condition that can be used to define failure. The specific nature of the failure condition generally is an important factor in resolving or avoiding wear failures. It can affect not only the solutions to a wear problem but also the details of the approaches used to obtain a solution (Bayer, n.d.).
16 3.2 Abrasive wear
Abrasive wear occurs when a hard rough surface slides across a softer surface. ASTM International (formerly the American Society for Testing and Materials) defines it as the loss of material due to hard particles or hard protuberances that are forced against and move along a solid surface.
Abrasive wear is classified according to the type of contact and the contact environment. The type of contact determines the mode of abrasive wear. The two modes of abrasive wear are known as two-body and three-body abrasive wear. Two-body abrasive wear is demonstrated by the action of sand paper on a surface. Hard asperities or rigidly held grits pass over the surface like a cutting tool. In three-body abrasive wear the grits are free to roll as well as slide over the surface, since they are not held rigidly. The two and three-body modes of abrasive wear are illustrated schematically in figure 3.1 (Kovaříková, Szewczyková, Blaškoviš, Hodúlová & Lechovič, n.d.).
Until recently these two modes of abrasive wear were thought to be very similar; however, some significant differences between them have been revealed. It was found that three-body abrasive wear is ten times slower than two-body wear since it has to compete with other mechanisms such as adhesive wear.
Figure 3.1: Two and three-body modes of abrasive wear (Granger & Blunt, 1998)
17 In many engineering applications, such as mining, metallurgy and agriculture, equipment fails because of abrasive wear. According to the ministry of Research and Technology, the percentage cost of abrasive wear in the metallurgy industry in the Federal Republic of German is 40 percent, with 30 percent in the mining industry, 20 percent in agriculture and 10 percent in production engineering.
The material that is most being used in India in metallurgical mining and agriculture industries is a plain carbon steel. Particularly mild steel is widely used in agriculture agro machinery industries for the fabrication of agricultural equipment and critical parts, and therefore which wears fast when subjected to high load and abrasive conditions. The present work has been devoted to assessing the suitability of adequate material properties and structure for agriculture industries (Kumar Jain & Singh, 2012).
3.3 Adhesive wear
This type of wear is synonymous with galling, fretting, scuffing or surface fatigue, and is described as the interaction and adhesion between surface irregularities. It is shown in figure 3.3 that if the strength of the adhesion junction is more than that of either one of the materials, material transfer and the production of wear particles will occur. The interaction between the materials is complex due to the high strain rates and temperatures being generated (Wear and hardness, 2013).
Adhesion in metals can be classified as mild or severe. Mild adhesion includes visible oxidation, wear of non-metallic debris, and low loads and velocities. Severe adhesion is characterised by damage to the oxide film so that there is direct interaction of the metal with the environment, larger wear particles, and higher loads and velocities. Adhesive wear generally occurs when inadequate lubrication leads to metal transfer (Wear and hardness, 2013).
Adhesive wear thus occurs due to the differences in hardness of the two interacting surfaces. In order to design for adhesive wear-resistance, dissimilar materials that are tribologically compatible should be considered (Wear and hardness, 2013).
Fretting wear is the repeated cyclical rubbing between two surfaces. Over a period of time this will remove material from one or both of the surfaces in contact. Fretting typically occurs in bearings, although most bearings have their surfaces hardened to resist the problem (Wear and hardness, 2013).
18
Another problem occurs when cracks in either surface are created, and this is known as fretting fatigue. It is the more serious of the two phenomena because it can lead to catastrophic failure of the bearing. An associated problem occurs when the small particles removed by wear are oxidised in air. The oxides are usually harder than the underlying metal, so wear accelerates as the harder particles abrade the metal surfaces further. Fretting corrosion acts in the same way, especially when water is present. Unprotected bearings on large structures like bridges can suffer serious degradation in behaviour, especially when salt is used during winter to de-ice the highways carried by the bridges (Wear and hardness, 2013)
Figure 3.2: Schematic illustration of adhesive wear (Grainger & Blunt, 1998)
3.4 Erosive wear
Erosion is defined in the ASM Handbook of Thermal Spray Technology as damage to a surface when a gas or liquid, ordinarily carrying entrained particles, impacts on that surface with velocity. In other words, erosion has magnitude (the particles impacting on the surface) and velocity, with the particles impacting on the surface at different angles (angle of impingement). If the angle of impingement is relatively small, the wear-producing mechanism closely resembles abrasion. When the angle of impingement is normal relative to the surface, material is displaced by plastic deformation, or dislodged by brittle failure. The effect of the angle of impingement is shown in figure 3.3 (Wear and hardness, 2013).
19 Figure 3.3: Illustration of the different types of erosive wear
(Grainger & Blunt, 1998)
a) Abrasion at low impact angles
b) Surface fatigue during low speed, high impingement angle impact
c) Brittle fracture or multiple deformations during medium speed, large impingement angle impact
d) Surface melting at high impact speeds e) Macroscopic erosion with secondary effects f) Crystal lattice degradation from impact by atoms
20 Chapter 4 Methods of Wear Testing
4.1 Traditional methods
Most of the previous wear studies have focused mainly on surface damage in terms of material-removal mechanisms, including transfer film, plastic deformation and brittle fracture. This chapter describes the methods of wear testing on coated material. Most of the research in this chapter refers to coatings applied to cutting tools and the performance of the different materials being cut.
The need to evaluate the properties of new raw materials and substrate-coating combinations is important in view of developments in surface engineering design. Recently, experiments and testing on coated materials have been done, and some standardised and experimental test equipment has been produced to meet wear resistance specifications. Standard test methods such as pin-on disc are used extensively to simulate rubbing action in which plastic yielding occurs at the tip of individual sharpness. This testing is carried out mainly on a microscopic scale. Coatings such as those formed in thermal spraying seldom experience penetration during the carrying out of some of the standard wear tests that are available. It is unclear whether behavioural models developed for thin, hard coatings necessarily apply to thicker coatings. Very few research papers could be found that investigate the type of wear occurring under combined impact and sliding wear which suggests that it has hardly been studied.
4.2 Wear of engineering material
There are many types of wear, as indicated in chapters two and three, which are of concern to the user of coatings, including sliding wear and friction, low- and high-stress abrasion, dry particle erosion, and slurry erosion. Reducing the coefficient of friction has many advantages in machining processes. In practice it is possible for a coating to wear and the substrate to be unaffected. Also, the substrate may deform without any noticeable wear of the coating. It is claimed and confirmed from practice, that hard coatings applied to cutting tools increase tool life by two to ten times that of uncoated tools. Hard coatings have some disadvantages, which include porosity, insufficient bonding to the substrate and, in some cases have limited thickness. Coatings experience shear, tensile and compressive stresses which may lead to failure by cracking. In applications of material wear, one or more of the following will be
21 operational: abrasive wear, adhesive wear, erosive wear, fretting wear and surface fatigue (Kennedy & Hashmi, 1998).
4.3 Wear test methods
In selecting a suitable wear test, there are a few points that should be considered. First, ensure that the test selected is measuring the desired properties of a material. Second, confirm whether the material is in bulk form or is a thick or thin coating. Third, establish whether the forces and stress limits are suitable for the test. Fourth, confirm whether abrasives are present and consider the abrasive size, form and velocity. Fifth, check whether the contact between the components is rolling, sliding, impact or erosion only, or a combination of these, bearing in mind that the surface finish of the test samples should be similar to that of the actual components. Then lastly, establish whether temperature and humidity factors are important and whether the test environment is similar to the actual working environment.
Tests are used for quality control functions such as thickness, porosity, adhesion, strength, hardness, ductility, chemical composition, stress and wear resistance. Many tests for coated and uncoated cutting tools are conducted on machine tools, including lathes, mills, drills, punches and saws. These test methods provide almost identical conditions to those experienced in manufacturing. Machining tests subject cutting tools to many wear parameters, including impact and shock, abrasion, adhesion and hot corrosion. The limitations of these tests depend on the machine power available and the quality of the machine tool (Kennedy & Hashmi, 1998).
4.3.1 Abrasive and adhesive test equipment
Hardness is often used as an initial guide to the suitability of coating materials for applications requiring a high degree of wear resistance. The effect of the hardness of a wearing material however is complicated, as different wear mechanisms can prevail in service. Scratch hardness is the oldest form of hardness measurement. Mohs in 1822 categorised materials using this process, giving diamond a maximum scratch hardness of ten. Most scratch type tests developed from this simple technique. In indentation adhesion tests, a mechanically stable crack is introduced into the interface of the coating and substrate. The resistance to propagation of the crack along the interface is used as a measure of adhesion. In scratch-adhesion tests, a stylus is drawn over the surface under a continually increasing normal load until the coating fails (Ludema, 1994).
22 4.3.2 Pin-on-disc
Pin-on-disc was the most widely used wear test processes, followed by pin-on-flat, according research conducted by Glaeser and Ruff. Other applications of pin-on-disc include material wear and friction properties at elevated temperatures and in controlled atmospheres. In a two-body abrasion test, a coated pin is pressed against a rotating abrasive paper making a spiral path to avoid overlapping. This test process is very common for thin coatings. There is also some research done on using a diamond tip as the abrading tool in a pin-on-disc test to operate within the chamber of a Scanning Electron Microscope (SEM) to examine abrasion effects. Scratch testing in conjunction with SEM provides a useful method of analysing single-point wear mechanisms of coated systems through an assessment of the deformation and fracture produced (Ludema, 1994).
4.3.3 Rubbing tests
An ASTM standard uses a crossed-cylinder apparatus for testing similar and dissimilar metals and alloys and coated systems under unlubricated conditions. A rotating cylinder is forced at right angles against a stationary cylinder. The volume of material loss is determined by means of an appropriate equation (Kennedy & Hashmi, 1998)
4.3.4 Taber tests
The Taber Abraser, ASTM 1044, is used to measure the low-stress abrasive wear resistance of materials and coatings. Low-stress abrasive wear occurs when hard particles are forced against and move along a flat, solid surface where the particle loading is insufficient to cause fracture of the hard particles. Two- and three body abrasive wear can be assessed with this method. The Taber apparatus is shown in Figure 4.1. The specimen, which is coated or uncoated, is rotated, causing the abrasive wheels to drag and abrade the surface. Wear is normally determined by weight loss (Kennedy & Hashmi, 1998).
23
Figure 4.1: Schematic diagram of the Taber abrasion apparatus (Kennedy & Hashmi, 1998)
4.4 Experiment theory
If wear tests are carried out with a high degree of simulation of the service situation, then the results can be used with considerable confidence in selecting the best wear-resistant coating system. Every wear test, whether for bulk material or coatings, can be complicated by equipment problems, test procedures, sample preparation, inconsistency in abrasive materials and the wrong interpretation, of the test information. Thin coatings require greater care in wear tests in order to avoid penetration, which requires lighter loads and shorter test durations. Surface roughness also influences the tribological performance of a mechanical system. The contours of abrasion or wear scars may make mathematical methods of calculating the wear scar inaccurate. In this event, adhesive tapes used for surface profile or roughness assessment may be used. It is also important to use a simple shape for the abrading tool, such as a hemispherical shape, for the test process. The benefits of applying surface coatings to reduce wear can be measured in many practical ways such as machine efficiency, reduced power requirements and longer running life (Kennedy & Hashmi, 1998).
Specimen
Drive
Rubber bonded abrasive wheels
24 Chapter 5 Performance Enhancement Strategies
5.1 Opportunities in plastic
The standards for agriculture and construction equipment are constantly rising. Tighter emissions standards are stipulated, and longer durability and serviceability are required. Balancing the demands of the application with cost and styling considerations has led to an increased use of engineering thermoplastics which is where the strong, tough, durable and lightweight materials give engineers the ability to design products that meet their expectations.
Farming and construction equipment represent a huge investment which increasingly needs to be maximised. For manufacturers, the quest continues to find materials that can contribute to the increasing sophistication and functionality of modern farming and construction equipment while being able to withstand the harsh demands of the application and keeping systems costs as low as possible.
In the case of harvesters and planters where high fatigue and abrasive wear are issues, in some cases plastics have been shown to outperform metal. In many applications in the agriculture and construction equipment market, when compared to metal, engineering thermoplastics offer the advantage of design freedom, corrosion resistance and weight reduction. Stanyl is an extremely hard-wearing, heat-resistant PA46 thermoplastic used for friction reduction in outdoor power equipment applications.
5.1.1 Stanyl wear and friction applications
Agriculture and construction equipment must operate efficiently in some of the most demanding environments on earth, from the Arctic Circle to the deserts, and the tropics. In all these environments one of the greatest challenges is minimising the wear and friction on moving parts. Wear, and especially abrasive wear, is the cause of failure of many moving parts in agriculture and construction equipment. Stanyl polyamide-46 is best-in-class among engineering thermoplastics in its resistance to abrasion. Using Stanyl in the critical moving parts for agriculture and construction equipment can lead to extended life, improved performance, weight reduction, reduced emissions and lower total cost.
25 Stanyl is a high-performance polyamide-46 that retains its mechanical properties at long term temperatures of up to 230˚C. It offers excellent stiffness at elevated temperatures, plus extended fatigue endurance and outstanding wear resistance which are perfect for friction reduction applications as well as harsh agriculture and construction environments (Stanyl, n.d).
Increasingly, outdoor power equipment components need to perform at a high level and at higher temperatures (in excess of 230˚C). Stanyl is ideal therefore for under-the-hood components because of its ability to outlast metal and other traditional materials. It also provides excellent wear and friction resistance in timing chain tensioners and equally good abrasion resistance for moving parts such as harvester forks. All of which makes it an ideal replacement for Polyphthalamide (PPA), Polyamide 6T (PA6T), Polyamide 9T (PA9T) and often Polyphenylene sulfide (PPS) and Liquid Crystal Polymer (LCP) (Stanyl, n.d).
Products in this sector take tremendous punishment and need to be tough and durable with great wear and friction properties. These next-generation plastics are robust and lighter than metal. This means that less material is needed and fuel consumption is lower. They are robust and operate well under stress and at extreme temperatures, especially in and around the engine. In fact plastics like Stanyl and polyamide 6 can last up to three times longer than metals in some applications (Stanyl, n.d).
5.2 Rubber and urethane
Rubber and urethane application can significantly reduce wear and tear on agricultural machinery and livestock equipment. Rubber sheets and matting can be used for livestock stalls, trailers, veterinary rooms or other areas to protect assets. Urethane lining is applied to metal tanks, farm equipment, piping and spouts to reduce the abrasion and corrosion that limits the life of the equipment (Rubber & Urethane Products Extend the Life of Equipment in the Agricultural Industry, n.d).
5.2.1 Tuff-Tube spout lining
The Tuff-Tube lining system is a patented urethane spout liner that significantly reduces the abrasion of grain, seed and fertiliser handling and extends the life of agriculture equipment. In a season or less grain will cause extreme wear in spouting which can ruin the spouting. The Tuff-Tube lining system is an excellent answer to high maintenance costs and the constant replacement of steel spouts. The Tuff-Tube spouting liner can be rotated 120° to
26 180° to present additional wear surfaces. Fully used liners can be removed and replaced using the same steel spout which saves the expense of having to purchase a new spout each year. The Tuff-Tube lining system reduces costs and protects valuable machinery (Urethane Spout Liner to Protect Equipment from Extreme Spouting Wear, n.d).
This is a seamless spouting system that prevents objects from getting in between the liner and spout preventing buckling, plugging and peeling issues. The lined spout elbows have a permanently bonded liner that matches up to the Tuff-Tube liner for total spout protection (Urethane Spout Liner to Protect Equipment from Extreme Spouting Wear, n.d).
Figure 5.1: Applications of Tuff-Tube Spout Lining (Urethane Spout Liner to Protect Equipment from Extreme Spouting Wear, n.d)
5.2.2 Spray urethane
Urethane coatings are used to protect against friction, chemical attack and weather wear on agriculture equipment. Urethane can increase the life of equipment due to its plastic elastomer nature. Industrial urethane coatings will bond to the equipment as they are flexible and will shrink or expand with the substrate. Paint on the other hand lacks flexibility and will break its bond when flexed. Industrial spray urethane shields against abrasion, impact, and the abuse from the elements. Some applications where urethane is used are dump trucks to increase load release, soybean dryers, frame rails for soybean sorters and hoppers (Urethane Spout Liner to Protect Equipment from Extreme Spouting Wear, n.d).
27
Figure 5.2: a) 40 ton dump truck with urethane for increased load release b) Lined steel hopper (Urethane Spout Liner to Protect Equipment from Extreme
Spouting Wear, n.d)
5.3 Rubber sheets
Rubber faced steel plates prevent damage when steel meets steel or is unprotected against friction, abrasion and corrosion. Tests have shown that rubber faced plates have an abrasion wear time up to 10 times longer than unprotected metals. Abrasiplate or “rubber-face plate” is not simply a piece of sheet rubber glued to metal. The vulcanisation process and specially formulated rubber compound results in a blister free, virtually unbreakable bond between rubber and metal. This technology is used in grain-handling applications like spouts, hoppers and elbows and the transition can be lined with rubber for increased life of the part and reduced grain breakage (Rubber & Urethane Products Extend the Life of Equipment in the Agricultural Industry, n.d.).
Figure 5.3: Assorted rubber plates (Rubber & Urethane Products Extend the Life of Equipment in the Agricultural Industry, n.d)
28 5.4 Thermal spray coating technology
Thermal spraying consists of a group of coating processes in which finely divided metallic or non-metallic feed materials are melted or heated and then sprayed on to a surface to form a protective coating. The feed material may be in the form of a powder, a ceramic rod, wire or molten material. These coating materials are generally classified as pure metals, metal alloys, ceramics, ceramic metal composites or carbide coatings.
Virtually any material that can be produced in wire or powder form can be processed into a coating, which means that there are literally thousands of possible coatings available. A monolithic material and its equivalent coating do not necessarily have the same properties and most materials are actually degraded during the coating process. The same material can also be applied as a coating using different coating processes to produce coatings with very unique functional properties such as low or high coefficients of friction, electrical or thermal insulation and non-stick properties (An introduction to thermal spray, 2013)..
Before coating a metal, there are a few factors that must be considered. The purpose of the coating must be clear, for instance, to interpose a corrosion resistance between metal and the environment. The coating may consist of another metal, like zinc or tin coatings on steel, or a protective coating derived from the metal itself, like aluminium oxide, or organic coatings, such as resins, plastics and paints. The action of protective coatings is often more complex than simply providing a barrier between metal and the environment. Paints may contain a corrosion inhibitor (An introduction to thermal spray, 2013)..
5.4.1 Coating processes
Wire flame spray. With the wire flame spray process, the wire spray material is melted in a gaseous oxygen-fuel flame. The fuel gas can be acetylene, propane or hydrogen. The wire is fed concentrically into the flame, where it is melted and atomised by the addition of compressed air that also directs the melted material towards the work piece surface (An introduction to thermal spray, 2013).
Powder flame spray. The process for powder flame spray is exactly the same as wire flame spray in section 4.6.1. Powder is just used in the place of wire.
